Very small particles, such as micron-sized bacterial spores and oil droplets, can be difficult to separate from host fluids. Porous filters are sometimes used to separate such particles; however, such filters suffer from many defects. For example, the filters can be overly selective by filtering a large array of particles. Conversely, the filters can be too fine which results in selected particles passing through the filters. In either event, such filters require periodic cleaning and/or replacing which can be costly and disruptive to processes using the filters.